1. Field of the Invention
The present invention provides a nanoclay based solid sorbent comprising a nanoclay with at least one surface, and at least one amine containing compound wherein said amine containing compound is attached to said surface. A method of making this nanoclay based solid sorbent is also provided. A method of capturing carbon dioxide gas comprising passing a gas from an effluent process stream containing carbon dioxide through the nanoclay based solid sorbent of this invention is provided for capturing the carbon dioxide on and within the nanoclay. Regeneration of the nanoclay based solid sorbent by at least one cycle of desorption of the captured carbon dioxide gas from the nanoclay is provided.
2. Description of the Background Art
Capture of carbon dioxide is considered as an important step in reducing the emission of greenhouse gases. Solid sorbents are one means of achieving carbon capture. To make an effective solid sorbent for carbon dioxide sorption, a high surface area base material is required on which a chemical moiety is immobilized; this reacts with carbon dioxide molecules to achieve separation. A temperature swing or pressure swing method can be used to regenerate the solid sorbent. Current solid sorbents are problematic. The current sorbents are expensive to produce since they use expensive solid base material and therefore, they cannot be produced in large enough quantities to be used in existing plants where thousands of pounds of solid sorbents may be required per day. Also, many existing solid sorbents do not have high carbon dioxide capture capacity.
A solid sorbent using easily available low cost materials would be a large improvement in the ability to capture carbon dioxide. Additionally, the ability to make solid sorbents which can be produced on large scales using well-established industrial methods is needed.
Nanoclays are primarily used to make polymer nanocomposites and as viscosity modifiers in various products such as drilling fluids and skin-care products. They are very low-cost compared to other nano-sized products such as carbon nanotubes. These clays cost only few dollars a pound as compared to hundreds or thousands dollars a pound for more exotic materials like metal organic frame works or carbon nanotubes. The nanoclays can also be mined and then processed in very large quantities compared to other solid sorbents which can be produced only in limited amounts.
A variety of solid sorbents have been evaluated for use with post-combustion flue gases. For example, porous silica grafted with amines (Chang et al., 2003; Gray et al., 2005; Hiyashi et al., 2005; Khatri et al., 2005; Zelenak et al., 2008), amine grafted molecular baskets of silica aerogels (Huang et al., 2003; Xu et al., 2003), porous PMMA beads with immobilized amines (Gray et al., 2007; Lee et al., 2008), porous alumina with amine (Plaza et al., 2008) and fly ash with grafted amine (Gray et al., 2004) have been investigated as CO2 solid sorbents.
For the existing solid sorbents mentioned above, reported adsorption capacities vary widely from about ˜200 mmol CO2/gm to ˜4000 mmol CO2/gm (˜0.9 wt % to ˜18 wt %) of sorbent. It has been suggested that the sorbent should have at least 2000 mmol/gm (˜9 wt %) long term capture capacity to be considered as a viable candidate for practical use (Chang et al., 2003). However, it should be noted that the CO2 capture capacity is not the sole criterion for choosing a viable candidate for use at the industrial level. Several other criteria such as availability in large quantity, low cost and ease of production are important benchmarks as well in developing a usable solid sorbent. Current methods of making these solid sorbents are not scalable, however the proposed invention can be produced at large scale using well-established industrial methods. The proposed invention is very low cost compared to other products in the field, which gives this invention very significant advantage over other technologies. Additionally, many existing solid sorbents do not have high carbon dioxide capture capacity; this present invention achieves much higher capture capacity.
In spite of the background art, there remains a very real and substantial need for a nanoclay-based solid sorbent for capturing carbon dioxide gas, for example but not limited to the carbon dioxide gas that is contained in an effluent process stream.
Current solid sorbents suffer from the following problems: they are expensive to produce since they use expensive solid base material, and they cannot be produced in large enough quantities to be used in existing plants where thousands of pounds of solid sorbents may be required per day.